Three special emphases were planned to receive attention in 1999:

Seismic Hazard Estimation

SCEC's "Phase III" report will describe a suite of seismic source models for southern California, examine models for local site effects, describe the effect of 3-D wave propagation in sedimentary basins, show representative seismograms for scenario earthquakes, and discuss uncertainties and sensitivity to assumptions in seismic hazard estimation. In addition, the report will present several data bases, including an earthquake catalog, fault slip rate table, soil map, and theoretical seismograms. Research during 1998 will include follow-up studies to archive data bases, programs, and other material from the report, make them available on the World Wide Web, and participate in workshops and other events to explain the implications of the report to users. Further research will employ the results of the Phase III report, and special projects will be undertaken that will encourage the proper use of seismic hazard information in engineering practice, land use planning, and other applications.

3-D Seismic Velocity Model

Calculation of complete seismograms requires a model to evaluate P and S wave velocities at any arbitrary point in the medium through which seismic waves propagate. Rob Clayton of Caltech will organize an interdisciplinary project to construct a standard seismic velocity model satisfying a range of geophysical and geological observations, including strong motion seismograms, earthquake travel times, borehole geologic data, etc. The model will include the effects of sedimentary basins and near-surface sediments. The model will be used for calculation of theoretical seismograms, as well as theoretical calculations of stress increments from earthquakes and tectonic motions.

Stress Evolution

Earthquakes result from stress release on faults, and one desired feature of the Master Model is a facility for calculating the stress accumulation from past earthquakes, tectonics, and viscoelastic stress relaxation. Recent SCEC products, including a catalog of earthquake focal mechanisms for M6 earthquakes since 1850, and the horizontal crustal deformation map determined from geodetic observations provide relevant constraints for models of stress evolution. Research on this subject may include calculation of time-dependent stresses, comparison of earthquake occurrence (including aftershocks) with the local stress field, and testing of hypotheses following from the models. Theoretical studies may involve construction of theoretical models of stress evolution and adjusting parameters for agreement with geologic, geodetic, and seismic data. Observational studies may involve in-situ stress measurements, geological measurements of displacement patterns in past earthquakes, geodetic measurements of strain rate where it may reveal stress interactions, and seismic measurements of earthquake locations, focal mechanisms, and other observables relevant to the relationship between stress and earthquakes.

1999 Research Summaries